(1) Field of the Invention
The present invention relates to a buoyancy system for an aircraft, and to an aircraft provided with a buoyancy system.
The invention is thus situated in the technical field of buoyancy systems enabling an aircraft to alight on water and enabling it to float in stable manner, and it relates more particularly to a rotary wing aircraft.
(2) Description of Related Art
Such a buoyancy system contributes to providing an aircraft with buoyancy and stability after alighting on water. The buoyancy system may be used for example as a result of forced ditching at sea, in order to enable the occupants to evacuate the aircraft. All aircraft that fly missions for transporting people over the sea are in principle provided with such a buoyancy system.
Furthermore, certification regulations specify that an aircraft must be capable of alighting and being stable on water when using its buoyancy system. Stability must be confirmed for states of the free surface of the water and for wind levels that are defined in those certification regulations.
Such surface states for the water are also referred to as “sea states” and they apply to any liquid surface. Use of the term “sea” thus also covers an aircraft alighting on any free water surface, whether at sea proper, or on a lake, for example.
A buoyancy system may comprise floats that are deployed either on command of the pilot and/or copilot, for example, or else by automatic triggering, in particular by using one or more immersion detectors. Such floats may comprise bags that are inflated by deployment means that may be explosive or electrical, for example.
Floats may be arranged in pairs. Each pair of floats thus comprises two floats arranged transversely on opposite sides of the fuselage of the aircraft. The transverse space between the two floats may be referred to for convenience as the inter-float space.
By way of example, a rotorcraft may have two pairs of floats.
Document JP 61-171699 and Document US 2003/057322 disclose a buoyancy system attached to a helicopter skid.
Such a buoyancy system may also include structural floats that are not inflatable.
Thus, the known buoyancy systems that are provided with floats that are fastened to a fuselage of an aircraft by the rigid rigging bands, i.e. that are non-stretch.
Document U.S. Pat. No. 3,467,343 describes a buoyancy system having vertical floats that are inflated by compressed air. The floats are provided with wheels that are operated by hydraulic actuators.
Furthermore, the aircraft can slope laterally under the effect of wind or waves. The floats present on the side towards which the aircraft tilts are pushed into the water, thereby increasing the righting torque exerted by the floats on the aircraft. The righting torque tends to right the aircraft.
Nevertheless, if a wave is large, the floats may become completely submerged. The righting torque then tends to decrease.
Starting from an extreme position in which the center of gravity does not overlie the inter-float space, the aircraft capsizes.
Document JP 2010 064697 (Nat Univ Yokohama) thus describes an aircraft having a fuselage and two floats. Means deform elastically in order to space the floats apart when alighting on water.
Document U.S. Pat. No. 2,271,065 (Claudius Dornier Jr) describes an aircraft having two retractable floats that are moved away from a fuselage prior to alighting on water.
Also known is Document U.S. Pat. No. 2,702,171.